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<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  姓：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>firstName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>lastName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  全名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>span</span><span class="token punctuation">&gt;</span></span>{{ firstName }}-{{ lastName }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>span</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span><span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span><span class="token punctuation">{</span>
      <span class="token literal-property property">firstName</span><span class="token operator">:</span><span class="token string">'张'</span><span class="token punctuation">,</span>
      <span class="token literal-property property">lastName</span><span class="token operator">:</span><span class="token string">'三'</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div><p><img src="https://hasakwebblogimg.oss-cn-hangzhou.aliyuncs.com/202303171948545.png" alt="image.png"></p> <ol start="2"><li><code>method</code>实现</li></ol> <p><strong>数据发生变化，模板就会被重新解析</strong></p> <div class="language-html line-numbers-mode"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>姓名案例_methods实现<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  姓：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>firstName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>lastName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  全名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>span</span><span class="token punctuation">&gt;</span></span>{{ fullName() }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>span</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span> <span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token literal-property property">firstName</span><span class="token operator">:</span> <span class="token string">'张'</span><span class="token punctuation">,</span>
      <span class="token literal-property property">lastName</span><span class="token operator">:</span> <span class="token string">'三'</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">methods</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token function">fullName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>firstName <span class="token operator">+</span> <span class="token string">'-'</span> <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>lastName
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br></div></div><ol start="3"><li><p>computed计算属性</p> <ol><li><p>定义：要用的属性不存在，需要通过已有属性计算得来</p></li> <li><p>原理：底层借助了Objcet.defineproperty()方法提供的getter和setter</p></li> <li><p>get函数什么时候执行？</p> <ul><li>初次读取时会执行一次</li> <li>当依赖的数据发生改变时会被再次调用</li></ul></li> <li><p>优势：与methods实现相比，内部有缓存机制（复用），效率更高，调试方便</p></li> <li><p>备注</p> <ul><li>计算属性最终会出现在vm上，直接读取使用即可</li> <li>如果计算属性要被修改，那必须写set函数去响应修改，且set中要引起计算时依赖的数据发生改变</li> <li>如果计算属性确定不考虑修改，可以使用计算属性的简写形式</li></ul></li></ol></li></ol> <div class="language-html line-numbers-mode"><pre class="language-html"><code>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>姓名案例_计算属性实现<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  姓：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>firstName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>lastName<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  测试：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>x<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>	// 这里修改 不会调 fullName的get方法
  全名：<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>span</span><span class="token punctuation">&gt;</span></span>{{fullName}}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>span</span><span class="token punctuation">&gt;</span></span> <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>br</span><span class="token punctuation">/&gt;</span></span>
  <span class="token comment">&lt;!-- 全名：&lt;span&gt;{{fullName}}&lt;/span&gt; &lt;br/&gt; --&gt;</span>
  <span class="token comment">&lt;!-- 全名：&lt;span&gt;{{fullName}}&lt;/span&gt; &lt;br/&gt; --&gt;</span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">const</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span> <span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token literal-property property">firstName</span><span class="token operator">:</span><span class="token string">'张'</span><span class="token punctuation">,</span>
      <span class="token literal-property property">lastName</span><span class="token operator">:</span><span class="token string">'三'</span><span class="token punctuation">,</span>
      <span class="token literal-property property">x</span><span class="token operator">:</span><span class="token string">'你好'</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">computed</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token comment">//完整写法</span>
      <span class="token comment">// fullName: {</span>
      <span class="token comment">// 	get() {</span>
      <span class="token comment">// 		console.log('get被调用了')</span>
      <span class="token comment">// 		return this.firstName + '-' + this.lastName</span>
      <span class="token comment">// 	},</span>
      <span class="token comment">// 	set(value) {</span>
      <span class="token comment">// 		console.log('set', value)</span>
      <span class="token comment">// 		const arr = value.split('-')</span>
      <span class="token comment">// 		this.firstName = arr[0]</span>
      <span class="token comment">// 		this.lastName = arr[1]</span>
      <span class="token comment">// 	}</span>
      <span class="token comment">// }</span>

      <span class="token comment">// 简写</span>
      <span class="token function">fullName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'get被调用了'</span><span class="token punctuation">)</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>firstName <span class="token operator">+</span> <span class="token string">'-'</span> <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>lastName
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br></div></div><h2 id="_1-10-侦听属性"><a href="#_1-10-侦听属性" class="header-anchor">#</a> <strong>1.10. 侦听属性</strong></h2> <div class="language-html line-numbers-mode"><pre class="language-html"><code>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>天气案例<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h3</span><span class="token punctuation">&gt;</span></span>今天天气很{{ info }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h3</span><span class="token punctuation">&gt;</span></span>
  <span class="token comment">&lt;!-- 绑定事件的时候：@xxx=&quot;yyy&quot; yyy可以写一些简单的语句 --&gt;</span>
  <span class="token comment">&lt;!-- &lt;button @click=&quot;isHot = !isHot&quot;&gt;切换天气&lt;/button&gt; --&gt;</span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>changeWeather<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>切换天气<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">const</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span><span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span><span class="token punctuation">{</span>
      <span class="token literal-property property">isHot</span><span class="token operator">:</span><span class="token boolean">true</span><span class="token punctuation">,</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">computed</span><span class="token operator">:</span><span class="token punctuation">{</span>
      <span class="token function">info</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">?</span> <span class="token string">'炎热'</span> <span class="token operator">:</span> <span class="token string">'凉爽'</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">methods</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token function">changeWeather</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isHot
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br></div></div><p><img src="https://hasakwebblogimg.oss-cn-hangzhou.aliyuncs.com/202303171951287.png" alt="image.png"></p> <h3 id="_1-10-1-侦听属性基本用法"><a href="#_1-10-1-侦听属性基本用法" class="header-anchor">#</a> <strong>1.10.1. 侦听属性基本用法</strong></h3> <p><code>watch</code>监视属性</p> <ol><li>当被监视的属性变化时，回调函数自动调用，进行相关操作</li> <li>监视的属性必须存在，才能进行监视，既可以监视<code>data</code>，也可以监视计算属性</li> <li>配置项属性<code>immediate:false</code>，<strong>改为 true</strong>，则初始化时调用一次 <code>handler(newValue,oldValue)</code></li> <li>监视有两种写法
<ul><li>创建<code>Vue</code>时传入<code>watch: {}</code>配置</li> <li>通过<code>vm.$watch()</code>监视</li></ul></li></ol> <div class="language-html line-numbers-mode"><pre class="language-html"><code>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>天气案例_监视属性<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h2</span><span class="token punctuation">&gt;</span></span>今天天气很{{info}}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h2</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>changeWeather<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>切换天气<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">const</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span> <span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token literal-property property">isHot</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">computed</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token function">info</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">?</span> <span class="token string">'炎热'</span> <span class="token operator">:</span> <span class="token string">'凉爽'</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">methods</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token function">changeWeather</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isHot
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token comment">// 方式一</span>
    <span class="token comment">/* watch:{		
			isHot:{
				immediate:true,
				handler(newValue,oldValue){
					console.log('isHot被修改了',newValue,oldValue)
				}
			}
		} */</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
  <span class="token comment">// 方式二</span>
  vm<span class="token punctuation">.</span><span class="token function">$watch</span><span class="token punctuation">(</span><span class="token string">'isHot'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>		
    <span class="token literal-property property">immediate</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span> <span class="token comment">// 初始化时让handler调用一下</span>
    <span class="token comment">//handler什么时候调用？当isHot发生改变时</span>
    <span class="token function">handler</span><span class="token punctuation">(</span><span class="token parameter">newValue<span class="token punctuation">,</span> oldValue</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'isHot被修改了'</span><span class="token punctuation">,</span> newValue<span class="token punctuation">,</span> oldValue<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br></div></div><h3 id="_1-10-2-深度侦听"><a href="#_1-10-2-深度侦听" class="header-anchor">#</a> <strong>1.10.2. 深度侦听</strong></h3> <ol><li>Vue中的watch默认不监测对象内部值的改变（一层）</li> <li>在<code>watch</code>中配置<code>deep:true</code>可以监测对象内部值的改变（多层）注意</li> <li>Vue自身可以监测对象内部值的改变，但Vue提供的watch默认不可以</li> <li>使用watch时根据监视数据的具体结构，决定是否采用深度监视</li></ol> <div class="language-html line-numbers-mode"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>天气案例_深度监视<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h3</span><span class="token punctuation">&gt;</span></span>a的值是:{{ numbers.a }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h3</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>numbers.a++<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>点我让a+1<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h3</span><span class="token punctuation">&gt;</span></span>b的值是:{{ numbers.b }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h3</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>numbers.b++<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>点我让b+1<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>numbers = {a:666,b:888}<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>彻底替换掉numbers<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
  {{numbers.c.d.e}}
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">const</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span> <span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token literal-property property">isHot</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
      <span class="token literal-property property">numbers</span><span class="token operator">:</span> <span class="token punctuation">{</span>
        <span class="token literal-property property">a</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
        <span class="token literal-property property">b</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
        <span class="token literal-property property">c</span><span class="token operator">:</span> <span class="token punctuation">{</span>
          <span class="token literal-property property">d</span><span class="token operator">:</span> <span class="token punctuation">{</span>
            <span class="token literal-property property">e</span><span class="token operator">:</span> <span class="token number">100</span>
          <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">watch</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token comment">// 监视多级结构中某个属性的变化</span>
      <span class="token comment">/* 'numbers.a':{
				handler(){
					console.log('a被改变了')
				}
			} */</span>
      <span class="token comment">// 监视多级结构中所有属性的变化</span>
      <span class="token literal-property property">numbers</span><span class="token operator">:</span> <span class="token punctuation">{</span>
        <span class="token literal-property property">deep</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
        <span class="token function">handler</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
          console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'numbers改变了'</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br></div></div><p><img src="https://hasakwebblogimg.oss-cn-hangzhou.aliyuncs.com/202303171953921.png" alt="image.png"></p> <h3 id="_1-10-3-侦听属性简写"><a href="#_1-10-3-侦听属性简写" class="header-anchor">#</a> 1.10.3. 侦听属性简写</h3> <p>如果监视属性除了<code>handler</code>没有其他配置项的话，可以进行简写</p> <div class="language-html line-numbers-mode"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>title</span><span class="token punctuation">&gt;</span></span>天气案例_监视属性_简写<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>title</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../js/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>root<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h3</span><span class="token punctuation">&gt;</span></span>今天天气很{{ info }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h3</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>changeWeather<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>切换天气<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text/javascript<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
  Vue<span class="token punctuation">.</span>config<span class="token punctuation">.</span>productionTip <span class="token operator">=</span> <span class="token boolean">false</span>
  <span class="token keyword">const</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span> <span class="token string">'#root'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">data</span><span class="token operator">:</span> <span class="token punctuation">{</span><span class="token literal-property property">isHot</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">computed</span><span class="token operator">:</span> <span class="token punctuation">{</span><span class="token function">info</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">?</span> <span class="token string">'炎热'</span> <span class="token operator">:</span> <span class="token string">'凉爽'</span><span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">methods</span><span class="token operator">:</span> <span class="token punctuation">{</span><span class="token function">changeWeather</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>isHot <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isHot<span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">watch</span><span class="token operator">:</span> <span class="token punctuation">{</span>
      <span class="token comment">// 正常写法</span>
      <span class="token comment">// isHot: {</span>
      <span class="token comment">// 	// immediate:true, //初始化时让handler调用一下</span>
      <span class="token comment">// 	// deep:true,	//深度监视</span>
      <span class="token comment">// 	handler(newValue, oldValue) {</span>
      <span class="token comment">// 		console.log('isHot被修改了', newValue, oldValue)</span>
      <span class="token comment">// 	}</span>
      <span class="token comment">// },</span>

      <span class="token comment">//简写</span>
      <span class="token function">isHot</span><span class="token punctuation">(</span><span class="token parameter">newValue<span class="token punctuation">,</span> oldValue</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'isHot被修改了'</span><span class="token punctuation">,</span> newValue<span class="token punctuation">,</span> oldValue<span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>

  <span class="token comment">//正常写法</span>
  <span class="token comment">// vm.$watch('isHot', {</span>
  <span class="token comment">// 	immediate: true, //初始化时让handler调用一下</span>
  <span class="token comment">// 	deep: true,//深度监视</span>
  <span class="token comment">// 	handler(newValue, oldValue) {</span>
  <span class="token comment">// 		console.log('isHot被修改了', newValue, oldValue)</span>
  <span class="token comment">// 	}</span>
  <span class="token comment">// })l</span>

  <span class="token comment">//简写</span>
  <span class="token comment">// vm.$watch('isHot', (newValue, oldValue) =&gt; {</span>
  <span class="token comment">// 	console.log('isHot被修改了', newValue, oldValue, this)</span>
  <span class="token comment">// })</span>
</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br></div></div><h3 id="_1-10-4-计算属性-vs-侦听属性"><a href="#_1-10-4-计算属性-vs-侦听属性" class="header-anchor">#</a> <strong>1.10.4. 计算属性 VS 侦听属性</strong></h3> <p><code>computed</code>和<code>watch</code>之间的区别</p> <ul><li><code>computed</code>能完成的功能，<code>watch</code>都可以完成</li> <li><code>watch</code>能完成的功能，<code>computed</code>不一定能完成，例如<code>watch</code>可以进行异步操作</li> <li>两个重要的小原则
<ul><li>所有被<strong>Vue</strong>管理的函数，最好写成普通函数，这样 <strong>this</strong> 的指向才是<code>vm</code>或组件实例对象</li> <li>所有不被<strong>Vue</strong>所管理的函数（定时器的回调函数、<strong>ajax</strong> 的回调函数等、<strong>Promise</strong> 的回调函数），最好写成**箭头函数，**这样 <strong>this</strong> 的指向才是<code>vm</code>或组件实例对象</li></ul></li></ul> <p><img src="https://hasakwebblogimg.oss-cn-hangzhou.aliyuncs.com/202303171956453.png" alt="image.png"></p> <h4 id="使用计算属性"><a href="#使用计算属性" class="header-anchor">#</a> <strong>使用计算属性</strong></h4> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token literal-property property">el</span><span class="token operator">:</span><span class="token string">'#root'</span><span class="token punctuation">,</span> 
    <span class="token literal-property property">data</span><span class="token operator">:</span><span class="token punctuation">{</span> 
        <span class="token literal-property property">firstName</span><span class="token operator">:</span><span class="token string">'张'</span><span class="token punctuation">,</span>
        <span class="token literal-property property">lastName</span><span class="token operator">:</span><span class="token string">'三'</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token literal-property property">computed</span><span class="token operator">:</span><span class="token punctuation">{</span>
    	<span class="token function">fullName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
		    <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>firstName <span class="token operator">+</span> <span class="token string">'-'</span> <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>lastName
    	<span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><h4 id="使用监听属性"><a href="#使用监听属性" class="header-anchor">#</a> <strong>使用监听属性</strong></h4> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>
<span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  <span class="token literal-property property">el</span><span class="token operator">:</span><span class="token string">'#root'</span><span class="token punctuation">,</span>
  <span class="token literal-property property">data</span><span class="token operator">:</span><span class="token punctuation">{</span>
    <span class="token literal-property property">firstName</span><span class="token operator">:</span><span class="token string">'张'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">lastName</span><span class="token operator">:</span><span class="token string">'三'</span><span class="token punctuation">,</span>
    <span class="token literal-property property">fullName</span><span class="token operator">:</span><span class="token string">'张-三'</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token literal-property property">watch</span><span class="token operator">:</span><span class="token punctuation">{</span>
    <span class="token function">firstName</span><span class="token punctuation">(</span><span class="token parameter">val</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
      <span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>fullName <span class="token operator">=</span> val <span class="token operator">+</span> <span class="token string">'-'</span> <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>lastName
      <span class="token punctuation">}</span><span class="token punctuation">,</span><span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token function">lastName</span><span class="token punctuation">(</span><span class="token parameter">val</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
      <span class="token keyword">this</span><span class="token punctuation">.</span>fullName <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>firstName <span class="token operator">+</span> <span class="token string">'-'</span> <span class="token operator">+</span> val
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div></div></section> <footer class="page-edit"><!----> <!----></footer> <!----> <div class="comments-wrapper"><!----></div></main></div> <!----></div> <ul class="sub-sidebar sub-sidebar-wrapper" style="width:0;" data-v-b57cc07c data-v-7dd95ae2></ul></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-c6073ba8 data-v-c6073ba8><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-c6073ba8><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-c6073ba8></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-c6073ba8></path></svg></div></div></div>
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